<!DOCTYPE html>
<html lang="en">
    <head>
        <!--将viewport的宽度设置为设备的宽度，也就是设备独立像素-->
        <meta name="viewport" content="width=device-width, initial-scale=1">
    </head>
    <body style="margin:0">
    <div style="width:320px;height:320px;background-color:gray;">
        
    </div>
    </body>
</html>